Skip to main content
NCBI home page
RSC Advances logoLink to RSC Advances
. 2023 Mar 13;13(12):8114–8129. doi: 10.1039/d3ra01020a

Palladium Schiff base complex-modified Cu(BDC-NH2) metal–organic frameworks for C–N coupling†

Khadijeh Rabiei a,✉, Zahra Mohammadkhani a, Hassan Keypour b, Jamal Kouhdareh b
PMCID: PMC10014173  PMID: 36926010

Abstract

In this study, the synthesis of a novel functionalized metal–organic-framework (MOF) [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst via post-synthetic modification of Cu(BDC-NH2) is reported. The targeted complex was prepared by chemically attaching N,N′-bis(5-formylpyrrol-2-ylmethyl) homopiperazine via a Schiff base reaction followed by complexation with Pd ions. Afterwards, the synthesized solid was applied as a very effective multifunctional catalyst in C–N coupling reactions. The synthesized compounds were identified by suitable techniques including N2 isotherms, EDX spectroscopy, FT-IR spectroscopy, XRD, SEM, ICP-OES and TG-DTA. This nanocatalyst was used in C–N cross-coupling reactions, and it showed its usage in a diverse range of different functional groups with good efficiency. The reasons for introducing this catalyst system are its advantages such as considerably high selectivity, almost complete conversion of products, high yields, and convenient separation of catalysts and products. The results indicate that the highest efficiency of the product in the reaction was obtained in the shortest possible time with the use of [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalysts. Overall, the high catalytic activity of the [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst may be due to the obtained high surface area and the synergistic features created between Lewis acidic Cu nodes and Pd ions.

In this study, the synthesis of a novel functionalized metal–organic-framework (MOF) [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst via post-synthetic modification of Cu(BDC-NH2) is reported.graphic file with name d3ra01020a-ga.jpg

1. Introduction

Metal–organic frameworks (MOFs) are a new class of mesoporous compounds, which due to their properties, have many applications in areas such as gas storage,1,2 catalytic processes,3–6 drug delivery,7–9 encapsulation,10 supercapacitance,11 and heavy metal absorption.12 Not only do MOFs possess higher levels of activation and stability than those of other classes of porous materials, but they are also capable of altering void morphology and size. This is an advantage in terms of improved separation and selectivity in applications.13–15

Post-synthetic modification of metal–organic frameworks is a common and practical approach to access MOF-based catalysts with the advantage of having multiple active sites, making this class of materials attractive to researchers.16,17 Increasingly popular among designing and synthesizing new molecular scaffolds with unique structural and biological properties that enhance performance and selectivity is an interesting challenge. This MOF, a nanoporous compound, is stable under various conditions and can maintain its porosity as evidenced by its chemical and thermal robustness.18–20

In recent years, there have been numerous reports on the optimal performance of modified catalysts in MOF structures, including oxidation reactions, carbon–carbon coupling and reduction.21,22 Some functional reports suggest MOFs as more popular candidates than other porous nanostructures.23

The Pd catalyst is an effective heterogeneous catalyst for carbon–carbon (C–C)24 and carbon–nitrogen (C–N) coupling reactions,25 such as the Heck reaction and Suzuki–Miyaura reaction,26–30 reduction of nitroaromatic compounds31–33 and oxidation of alcohol to aldehyde,34 affording good to high yields. Our hopes for the approach of using metal–organic frameworks as catalyst supports provide a unique basis for the use of these mesoporous polymers in catalysis. A cross-coupling reaction is a transformation in which two fragments are joined together with the help of a metal catalyst. One of the most important reasons for using palladium-containing catalysts is their ability to carry out carbon–carbon and carbon–nitrogen cross-coupling reactions. N-Arylated compounds are available naturally and synthetically and have diverse applications in many fields.35,36 This class of reactions is known as among the most important transformations in the synthesis of active medicinal substances.37–46 Solid-phase organopalladium complexes in addition to high efficiency and activity have a very important feature of selectivity, which helps in improving the synthesis of organic molecules. One of the types of important reactions is carbon–nitrogen coupling.47,48

In this research, a new palladium Schiff-base complex modified based on modified Cu(BDC-NH2) metal–organic frameworks was designed and prepared. In the next step, after the synthesis of the Cu(BDC-NH2) metal–organic framework, it was used as a support to make an organopalladium nanocatalyst. This nanocatalyst was used in the study of reaction for the assembly of 1,3-disubstituted pyrrolo[1,2-α]pyrazines, which obtained very good results with high efficiency and excellent stability of the nanocatalyst.

2. Experiments

2.1. Catalyst preparation

Cu(BDC-NH2) was prepared according to the published method.49–51 2-Aminoterephthalic acid (NH2-BDC) (1.087 g) and copper(ii) nitrate (0.853 g) were added to a solution of dimethylformamide (DMF) (18 mL) and methanol (2 mL) transferred to a Teflon-lined stainless steel autoclave, stirred for 30 min, and then heated at 150 °C for 48 h. Next, Cu(BDC-NH2) was obtained after washing and drying overnight.

In the next stage, a N,N′-bis(5-formylpyrrol-2-ylmethyl) homopiperazine (A) ligand was prepared by a general method, as previously reported by Mani's group.52 Then, the surface of Cu(BDC-NH2) was functionalized with (A) to form Cu(BDC-NH2)@Schiff-base: 1 g of prepared Cu(BDC-NH2) was dispersed in dry ethanol (25 mL) by sonication for 30 min. Subsequently, a solution of ligand (3 mmol in dry ethanol (60 mL)) was added dropwise and the resulting solution was stirred for 24 h under reflux conditions. Afterward, the obtained Cu(BDC-NH2)@Schiff-base was collected by centrifugation, washed with dry ethanol, and dried at 80 °C in an oven for 3 h.

Subsequently, Cu(BDC-NH2)@Schiff-base (1.5 g) was dispersed in acetonitrile (30 mL) using an ultrasonic bath for 30 min. In the next step, a yellow solution of PdCl2 (50 mg, 2.8 mmol) in 25 mL of acetonitrile was added to the dispersed Cu(BDC-NH2)@Schiff-base and the mixture was stirred at room temperature for 24 h. Finally, Cu(BDC-NH2)@Schiff-base-Pd(ii) was separated by decantation and washed successively with acetonitrile, ethanol and acetone to remove the unattached substrates (Scheme 1).

Scheme 1. Schematic of the synthetic procedure of the [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst.

Scheme 1

Open in a new tab

2.2. Catalyst characterization

In this class of compounds, due to the large number and variety of functional groups, the number of peaks obtained in the spectrum is very high. This makes it impossible to properly interpret these graphs due to the overlap of the peaks (Fig. 1). The only help that these graphs provide is the connection of some peaks from the shift. Due to some limitations of detection techniques for the [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst, more accessible and desirable detection techniques should be used. The functional groups on the synthesized [Cu(BDC-NH2)@Schiff-base-Pd(ii)] solid were investigated by FTIR spectroscopy, which is shown in Fig. 1. The FTIR spectrum of Cu(BDC-NH2) represented major stretching vibrations at 3400–3600 cm−1 (OH stretching and NH), 1717 cm−1 (C Created by potrace 1.16, written by Peter Selinger 2001-2019 O stretching), and 1690 cm−1 (C Created by potrace 1.16, written by Peter Selinger 2001-2019 N). All these peaks show blueshifts as Pd comes in the complex in [Cu(BDC-NH2)@Schiff-base-Pd(ii)], which reveals that the Pd complex is formed successfully.

Fig. 1. FT-IR spectroscopy of Cu(BDC-NH2) (A), Cu(BDC-NH2) modified (B), and [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst (C).

Fig. 1

Open in a new tab

Since most materials exhibit diffraction patterns specific to their structure, compounds can be identified using off-the-shelf databases or using information from similar articles. The purity of the sample and the composition of impurities present can be determined from the diffraction pattern, which can be used to determine and correct the lattice parameters of the crystal structure.53

The XRD patterns of the prepared Cu(BDC-NH2), and [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalysts are shown in Fig. 2. The XRD pattern of the synthesized Cu(BDC-NH2) shows characteristic peaks at 5–32°. The XRD pattern of the Cu(BDC-NH2) represents a crystalline arrangement. Moreover, it demonstrates that the Cu(BDC-NH2) center is maintained after conjugation. The XRD pattern of the prepared [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst shows the characteristic peaks of the Cu(BDC-NH2) center at 2θ = 5–32°, and palladium characteristic peaks at 32°, 32.5°, 35° and 41°.49 Hence, these observations prove the successful conjugation of N,N′-bis(5-formylpyrrol-2-ylmethyl) homopiperazine and complexation of palladium species on the Cu(BDC-NH2) surface. The average particle size of the sample was estimated according to Scherer's formula, D = 0.9λ/β cos θ, where λ is the wavelength of the incident X-ray (0.154 nm), β is the full width of peak at half maxima and θ is Bragg's angle. The obtained value is 56 nm, consistent with the result measured from the SEM images54 (Fig. 2).

Fig. 2. X-ray diffraction (PXRD) pattern of Cu(BDC-NH2) (A) and [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst (B).

Fig. 2

Open in a new tab

Thermogravimetric analysis or thermal gravimetric analysis (TGA) is a method of thermal analysis in which the mass of a sample is measured over time as the temperature changes; by examining the curves of these patterns, the thermal stability of the compounds can be investigated.55 Thermogravimetric analysis (TGA) spectra were used to investigate the thermal stability of the prepared Cu(BDC-NH2) and [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst, as shown in Fig. 3. TGA shows weight loss up to 150 °C. This may be related to the evaporation of water molecules from the pores of the MOF and aromatic groups. After this weight loss, the weight remained unchanged up to 350 °C, indicating high thermal stability of the synthesized Cu(BDC-NH2) and [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst.

Fig. 3. Thermogravimetric analysis (TGA) for Cu(BDC-NH2) (blue) and [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst (red).

Fig. 3

Open in a new tab

To further characterize this palladium nanocatalyst sample, an extrapolated onset temperature can be calculated. This indicates the temperature at which weight loss begins. We use the extrapolated start temperature (T0) for the nanocatalysts because it is a reproducible temperature calculation and is specified for use with an extrapolated start temperature of 700 °C. This is the reason for the optimal thermal stability of this MOF-based synthetic nanocatalyst.

Scanning electron microscopy (SEM) is a technique that uses a focused beam of high-energy electrons to identify nanomaterials that produce distinct signals on the surface of solid samples (Fig. 4). Receiving these signals and processing the information obtained from them cause the electrons to interact with the sample, revealing information about the sample such as external morphology (texture), material orientation, crystal structure and chemical composition.56 In these images, crystal structures and palladium nanoparticles with modified ligands on the surfaces of these organic–metal frameworks can be clearly seen.

Fig. 4. Scanning electron microscopic (SEM) image of Cu(BDC-NH2) (A and B) and [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst (C and D).

Fig. 4

Open in a new tab

An energy-dispersive X-ray spectroscopy (EDS, EDX, EDXS or XEDS) system is an accessory to electron microscopy equipment (scanning electron microscope (SEM) or transmission electron microscope (TEM) equipment) and the imaging capability of the microscope, which identifies the sample. The spectrum produced by EDX contains a spectrum analyzed for the peaks of the elements that make up the actual composition of the sample, giving the types of atoms available and the percentage of these atoms in the sample structure. The spectrum of the synthesized nanocatalyst shows the presence of elements C, N, O, Cu, Cl and Pd, which can be a sign of the success of the desired synthesis complex (Fig. 5). The appearance of Au* atoms in this spectrum is due to the kinetic of the sample during detection.57

Fig. 5. Energy-dispersive X-ray (EDX) spectra of [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst.

Fig. 5

Open in a new tab

We applied elemental mapping to complete the study on the elemental composition and distribution of the [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst (Fig. 6).Moreover, the elemental mapping results are in good agreement with the EDX patterns. The elemental mapping image shows the well-uniform distribution of the exponential elements (Cu, N, O, C, Cl, and Pd) in the [Cu(BDC-NH2)@Schiff base-Pd(ii)] catalyst, confirming the synthesis of heterogenized [Cu(BDC-NH2)@Schiff base Pd(ii)] catalytic complexes. Furthermore, the distribution of Cu elements reveals the coordination of the resulting framework to the carboxylic acid groups and confirms the formation of the catalyst support. Furthermore, the distribution of C, N, O, Cl, and Pd species indicates that the final metal catalyst is uniformly coordinated to the Schiff base ligands and forms a Schiff base Pd shell on the catalyst support.

Fig. 6. X-ray mapping images of [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst.

Fig. 6

Open in a new tab

N2 adsorption/desorption techniques were used to determine the surface structural parameters. The N2 adsorption/desorption results are plotted in Fig. 7. The surface area obtained based on the BET isotherm is 136.16 m2 g−1 and the total pore volume of the catalyst is 0.182 cm3 g−1. The adsorption isotherm is of type III and the appearance of a hysteresis loop indicates the presence of mesopores in the sample.

Fig. 7. N2 adsorption–desorption isotherms of Cu(BDC-NH2) (A) and [Cu(BDC-NH2)@Schiff-base-Pd(ii)] catalyst (B).

Fig. 7

Open in a new tab

2.3. Catalytic performance

2.3.1. General procedure for the synthesis of products

The amount of [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50 mg) and p-tolylboronic acid (1.5 mmol) with 1-(2-oxo-2-phenylethyl)-1H-pyrrole-2-added carbonitrile (0.6 mmol) in 5 mL of dimethylformamide to Table 1. After stirring for 24 hours at 70 °C, the mixture was cooled and filtered. The filtrate was diluted with ethyl acetate (30 mL) and washed with saturated brine. The aqueous layer was extracted with ethyl acetate (30 mL). The separated organic layer was dried over Na2SO4, concentrated in vacuo and the crude product was purified by column chromatography (silica gel) using petroleum ether/ethyl acetate (100 : 1, v/v) to A pure A product was obtained.

Optimization of the C–N coupling reaction of p-tolylboronic acid with 1-(2-oxo-2-phenylethyl)-1H-pyrrole-2-carbonitrile using the [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst.
graphic file with name d3ra01020a-u1.jpg
Entry [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (mg) Solvent Temperature (°C) Yielda (%)
1 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (0) MeCN 100 0.0
2 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (10) MeCN 100 2.1
3 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (20) MeCN 100 3.8
4 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (30) MeCN 100 6.6
5 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (40) MeCN 100 12.5
6 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50) MeCN 100 20.6
7 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (60) MeCN 100 20.7
8 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50) Acetone 100 17.3
9 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50) Toluene 100 29.8
10 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50) Dioxane 100 43.2
11 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50) DMF 100 86.3
12 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50) DMF 90 86.5
13 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50) DMF 80 86.3
14 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50) DMF 70 86.0
15 [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50) DMF 60 62.2
Open in a new tab
a

Isolated yield.

Based on the data obtained in Table 1, the C–N coupling reaction first occurred in the absence of catalyst at a temperature of 100 °C (entry 1) at which no product was formed. The optimal weight of the [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (entry 6) is 50 mg. One of the parameters to optimize was the selection of suitable solvents for model reactions. According to the results of model reactions and optimization experiments, the highest efficiency of the C–N coupling reaction was obtained at a reaction temperature of 70 °C, a N,N-dimethylformamide (DMF) solvent volume of 5 mL, and a reaction time of 9 hours in an air atmosphere (Table 1, entry 14).

DMF will thermally decompose to give CO and dimethyl amine (presumably the method base is produced to deprotonate the ligands in MOF synthesis). This becomes more prominent at high temperatures. If you want to avoid formate formation, then you need to keep your reaction media scrupulously dry. We do this by using DMF from a solvent purification system and then using proper Schlenk technique.58

The [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst is used in the C–N coupling of p-tolylboronic acid and 1-(2-oxoethyl)-1H-pyrrole-2-carbonitrile carried out in DMF at 70 °C in an air atmosphere (Table 2, 3a–3h). Compound 1-(2-oxoethyl)-1H-pyrrole-2-carbonitrile can be prepared by reacting hydrogen, hydrogen, transformed by different substitutions at the position of the donating group, or electron donating group. Although there is no logical and direct relationship with the efficiency of the reaction, it directly affected the rate and kinetics of the reaction. The reaction proceeded more slowly in the presence of the group.

[Cu(BDC-NH2)@Schiff base Pd(ii)]-catalyzed N-arylation of 1-(2-oxoethyl)-1H-pyrrole-2-carbonitriles with p-tolylboronic acida.
graphic file with name d3ra01020a-u2.jpg
Entry R1 R2 Product Time (h) Melting point (°C) Appearance Yieldb (%)
1 graphic file with name d3ra01020a-u3.jpg graphic file with name d3ra01020a-u4.jpg graphic file with name d3ra01020a-u5.jpg 18 129 White powder 66%
2 graphic file with name d3ra01020a-u6.jpg graphic file with name d3ra01020a-u7.jpg graphic file with name d3ra01020a-u8.jpg 22 118 White powder 64%
3 graphic file with name d3ra01020a-u9.jpg graphic file with name d3ra01020a-u10.jpg graphic file with name d3ra01020a-u11.jpg 16 190 Brown powder 65%
4 graphic file with name d3ra01020a-u12.jpg graphic file with name d3ra01020a-u13.jpg graphic file with name d3ra01020a-u14.jpg 23 139 Dark green powder 83%
5 graphic file with name d3ra01020a-u15.jpg graphic file with name d3ra01020a-u16.jpg graphic file with name d3ra01020a-u17.jpg 16 100.5 White powder 71%
6 graphic file with name d3ra01020a-u18.jpg graphic file with name d3ra01020a-u19.jpg graphic file with name d3ra01020a-u20.jpg 17 127 White powder 85%
7 graphic file with name d3ra01020a-u21.jpg graphic file with name d3ra01020a-u22.jpg graphic file with name d3ra01020a-u23.jpg 22 170 Green powder 55%
8 graphic file with name d3ra01020a-u24.jpg graphic file with name d3ra01020a-u25.jpg graphic file with name d3ra01020a-u26.jpg 19 138 Brown powder 42%
Open in a new tab
a

Reactions were carried out in DMF at 70 °C for 24 h with the reaction components in the following ratio: p-tolylboronic acid (1.5 mmol), R1 in Table 2 derivatives (0.6 mmol), DMF (5 mL). [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst (50 mg).

b

Yield of the isolated product.

In Scheme 2, an acceptable mechanism for these reactions is proposed. In this mechanism, [Cu(BDC-NH2)@Schiff base Pd(ii)] reacts with aryl boric acid. Then, the cyano group forms the corresponding intermediate with the catalyst. Next, the aryl cyano group is condensed, and after that, the compound in question is synthesized by closing the ring and leaving the catalyst from the molecular structure.

Scheme 2. Proposed mechanism for the N-arylation reaction using [Cu(BDC-NH2)@Schiff base Pd(ii)].

Scheme 2

Open in a new tab

The catalytic properties of the [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst were compared with those of other catalysts in similar research articles. For this purpose, the results of these investigations are reported in Table 3. This catalyst had a higher efficiency than similar samples, and kinetically, the reactions occurred at a faster rate of progress. The new nanocatalyst is stable, non-toxic, economically viable, has simple synthesis steps, and is easily separated from the reaction.

Comparison of the effects of using different catalysts for the synthesis of products by C–N coupling.
Entry Catalyst Product Ref.
1 MCS-BAT-Cu(ii)-catalyzed 1-Aryl-5-amino-1H-tetrazoles 59
2 Magnetic γ-Fe2O3@Cu-LDH Quinolines 48
3 Pd/Cu-free co-catalyzed Abemaciclib and Fedratinib 60
4 PNP-SSS Buchwald–Hartwig C–N cross coupling 61
5 [Cu(BDC-NH2)@Schiff base Pd(ii)]catalyst 1-(2-Oxoethyl)-1H-pyrrole-2-carbonitriles with p-tolylboronic acid This work
Open in a new tab

Finally, it should be mentioned that the recycling and reuse of this nanocatalyst lead to a prospect for the synthesis of catalysts with a longer lifespan because the synthesis of this type of catalysts is expensive. It also requires special environmental conditions. After completing the reactions of the C–N coupling model, the catalyst can be easily separated from the reaction mixture by filtering and used in subsequent reactions by washing it several times with water and ethanol and drying it under vacuum (Fig. 8).

Fig. 8. Recycling performance of the [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst in the N-acrylate core of p-tolylboronic acid with derivatives R1 provided in Table 2 (entries 1–7).

Fig. 8

Open in a new tab

The recovery of the [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst in this study indicates a high-efficiency sequential application. The study of the XRD spectrum and scanning electron microscopic (SEM) images of the synthesized [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst after recovery shows the stability of this catalyst (Fig. 9). The Pd load in the material was found to be 7.54% and after recovery it was 7.33%, as estimated by the ICP-OES method.

Fig. 9. XRD spectrum of the [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst after recovery (A) and scanning electron microscopic (SEM) image of the [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst after recovery (B).

Fig. 9

Open in a new tab

After theoretical and experimental studies on these modified nanopolymers and proving their stability in reactions, it is necessary to use this class of compounds more than before.

2.3.2. General procedure for catalytic experiments

3-(Furan-2-yl)-1-(p-tolyl)pyrrolo[1,2-a]pyrazine (3a)

1H NMR (500 MHz, chloroform-d) δ 8.22 (s, 1H), 7.95 (d, J = 8.0 Hz, 2H), 7.51 (m, 1H), 7.46 (m, 1H), 7.35–7.33 (m, 2H), 7.00 (d, J = 4.0, 1H), 6.96–6.94 (m, 1H), 6.52–6.51 (m, 1H), 6.28–6.26 (m, 1H), 2.44 (s, 3H).

13C NMR (125 MHz, chloroform-d) δ 143.08, 141.92, 140.01, 131.06, 130.34, 129.31, 129.04, 128.98, 128.77, 116.20, 115.28, 111.90, 111.78, 107.29, 105.30, 21.60.

HRMS (ESI): m/z [M + H]+ calcd for C18H15N2O: 275.1179; found: 275.1205.

3-(Naphthalen-2-yl)-1-(p-tolyl)pyrrolo[1,2-a]pyrazine (3b)

1H NMR (500 MHz, chloroform-d) δ 8.46 (s, 1H), 8.21 (m, 1H), 8.01–7.94 (m, 3H), 7.80–7.84 (m, 2H), 7.77–7.72 (m, 1H), 7.44–7.35 (m, 3H), 7.27 (d, J = 8.0 Hz, 2H), 6.88–6.89 (m, 1H), 6.80–6.81 (m, 1H), 2.37 (s, 3H).

13C NMR (125 MHz, chloroform-d) δ 152.98, 139.92, 136.85, 135.94, 135.08, 133.81, 133.24, 129.33, 128.79, 128.56, 128.38, 127.76, 126.31, 126.23, 126.03, 124.98, 123.85, 115.90, 115.34, 115.34, 113.59, 104.62, 21.59.

HRMS (ESI): m/z [M + H]+ calcd for C24H19N2: 335.1543; found: 335.1555.

3-Phenethyl-1-(p-tolyl)pyrrolo[1,2-a]pyrazine (3c)

1H NMR (500 MHz, chloroform-d) δ 7.81–7.84 (m, 2H), 7.26–7.20 (m, 4H), 7.17–7.13 (m, 5H), 6.84–6.85 (m, 1H), 6.69–6.70 (m, 1H), 4.27 (s, 2H), 2.59 (s, 2H), 2.37 (s, 3H).

13C NMR (125 MHz, chloroform-d) δ 151.32, 139.39, 136.00, 135.92, 133.77, 129.33, 129.10, 128.69, 127.84, 127.08, 127.02, 122.50, 114.82, 113.28, 104.81, 34.48, 21.55, 20.40.

HRMS (ESI): m/z [M + H]+ calcd for C22H21N2: 313.1966; found: 313.1945.

1-(4-Methoxyphenyl)-3-phenylpyrrolo[1,2-a]pyrazine (3d)

1H NMR (500 MHz, chloroform-d) δ 8.18 (s, 1H), 8.09 (dd, J = 6.5, 2.0 Hz, 2H), 7.91 (m, 2H), 7.51 (dd, J = 2.5, 1.5 Hz, 1H), 7.27 (m, 3H), 7.06 (dd, J = 6.5, 2.0 Hz, 2H), 6.95 (m, 1H), 6.89 (dd, J = 4.5, 2.5 1H), 3.90 (s, 3H).

13C NMR (125 MHz, chloroform-d) δ 159.87, 151.26, 136.76, 135.89, 130.20, 129.08, 127.64, 126.82, 124.97, 124.87, 114.64, 114.08, 112.83, 111.91, 103.28, 54.38.

HRMS (ESI): m/z [M + H]+ calcd for C20H17N2O: 301.1335; found: 301.1323.

3-(2-Bromophenyl)-1-(p-tolyl)pyrrolo[1,2-a]pyrazine (3e)

1H NMR (500 MHz, chloroform-d) δ 8.11 (s, 1H), 7.98 (d, J = 8.0 Hz, 2H), 7.69–7.71 (m, 2H), 7.53–7.54 (m, 1H), 7.39–7.42 (m, 1H), 7.32–7.33 (m, 1H), 7.21–7.23 (m, 2H), 7.00 (m, 1H), 6.94–6.95 (m, 1H), 2.44 (s, 3H).

13C NMR (125 MHz, chloroform-d) δ 152.95, 139.86, 137.23, 135.74, 133.61, 132.04, 129.47, 129.33, 128.74, 127.65, 127.28, 124.01, 122.80, 117.10, 115.86, 115.50, 104.64, 21.60.

HRMS (ESI): m/z [M + H]+ calcd for C20H15BrN2: 363.0491; found: 363.0499.

3-Phenyl-1-(p-tolyl)pyrrolo[1,2-a]pyrazine (3f)

1H NMR (500 MHz, chloroform-d) δ 8.11 (s, 1H), 8.02 (dd, J = 8.0, 1.5 Hz, 2H), 7.83 (d, J = 8.0, 2H), 7.47–7.41 (m, 4H), 7.18 (d, J = 8.0 Hz, 2H), 6.87 (dd, J = 4.5, 1.5 Hz, 1H), 6.81 (dd, J = 4.0, 2.5 Hz, 1H), 2.32 (s, 3H).

13C NMR (125 MHz, chloroform-d) δ 151.72, 138.70, 136.72, 135.92, 134.77, 128.13, 127.63, 127.58, 126.82, 125.07, 124.87, 114.62, 114.12, 112.10, 103.32, 20.42.

HRMS (ESI): m/z [M + H]+ calcd for C20H17N2: 285.1386; found: 285.1376.

1-(4-Chlorophenyl)-3-phenylpyrrolo[1,2-a]pyrazine (3g)

Green solid; yield: 136.1 mg (49%); mp 169.8–170.1 °C.

1H NMR (500 MHz, chloroform-d) δ 8.14 (s, 1H), 7.98 (t, J = 2.0 Hz, 1H), 7.97 (t, J = 2.0 Hz, 1H), 7.94–7.89 (dd, J = 8.0, 1.0 Hz, 2H), 7.47–7.45 (m, 1H), 7.42 (t, J = 2.0 Hz, 1H), 7.38 (dd, J = 6.0, 2.0 Hz, 2H), 7.30–7.26 (m, 1H), 6.85–6.83 (m, 2H).

13C NMR (125 MHz, chloroform-d) δ 151.65, 137.56, 137.09, 137.01, 134.69, 130.13, 130.01, 129.59, 128.73, 128.65, 127.91, 115.52, 113.49, 103.28.

HRMS (ESI): m/z [M + H]+ calcd for C19H14ClN2: 305.0840; found: 305.0854.

1-(3-Chlorophenyl)-3-phenylpyrrolo[1,2-a]pyrazine (3h)

1H NMR (500 MHz, chloroform-d) δ 8.24 (s, 1H), 8.06 (dd, J = 6.5, 1.5 Hz, 2H), 8.00 (dd, J = 4.5, 1.5 Hz, 2H), 7.56–7.45 (m, 5H), 7.39–7.36 (m, 1H), 6.93–6.92 (m, 2H).

13C NMR (125 MHz, chloroform-d) δ 151.55, 137.50, 137.04, 137.01, 135.69, 130.10, 130.02, 129.59, 128.73, 128.05, 125.91, 125.87, 115.52, 113.49, 104.22.

HRMS (ESI): m/z [M + H]+ calcd for C19H14ClN2: 305.0840; found: 305.0864.

3. Conclusion

The [Cu(BDC-NH2)@Schiff base Pd(ii)] nanocatalyst was synthesized as a novel nanocomposite via a two-step post-synthetic modification reaction of Cu(BDC-NH2) with N,N′-bis(5-formylpyrrol-2-ylmethyl) homopiperazine followed by Pd ion immobilization.

The characterization of the [Cu(BDC-NH2)@Schiff base Pd(ii)] catalyst was done by ICP-OES, TG-DTA, FT-IR spectroscopy, EDX spectroscopy, XRD, and N2 isotherms. Other contributors are the cooperative effect between the amine sites and the large surface area, and the high porosity of MOFs. In addition, [Cu(BDC-NH2)@Schiff base Pd(ii)] was found to be a multifunctional MOF with robustness and stability under the reaction conditions. Accordingly, it can be reused up to seven times without losing its catalytic activity and structural integrity. The other benefits of the proposed mesoporous catalyst include high yields, facile separation of the catalyst from the mixture, and clean reaction profile. This research portrays a bright future of using porous MOFs and their functionalized analogs as multifunctional catalysts.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Supplementary Material

RA-013-D3RA01020A-s001

Acknowledgments

Funding of our research from the Qom University of Technology is gratefully acknowledged.

†

Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d3ra01020a

References

  1. Daglar H. et al., Effect of metal–organic framework (MOF) database selection on the assessment of gas storage and separation potentials of MOFs. Angew. Chem., Int. Ed. 2021;60(14):7828–7837. doi: 10.1002/anie.202015250. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Alezi D. et al., MOF crystal chemistry paving the way to gas storage needs: aluminum-based soc-MOF for CH4, O2, and CO2 storage. J. Am. Chem. Soc. 2015;137(41):13308–13318. doi: 10.1021/jacs.5b07053. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Liu J. et al., MOF-enabled confinement and related effects for chemical catalyst presentation and utilization. Chem. Soc. Rev. 2022;51:1045–1097. doi: 10.1039/D1CS00968K. [DOI] [PubMed] [Google Scholar]
  4. Ghobakhloo F. et al., Copper (II) Schiff-Base Complex Modified UiO-66-NH2 (Zr) Metal–Organic Framework Catalysts for Knoevenagel Condensation–Michael Addition–Cyclization Reactions. Inorg. Chem. 2022;61(12):4825–4841. doi: 10.1021/acs.inorgchem.1c03284. [DOI] [PubMed] [Google Scholar]
  5. Kouhdareh J. Keypour H. Alavinia S. Anchorage of Pd into Modified Isoreticular Metal–Organic Framework-3 as a Heterogeneous Catalyst for Mizoroki–Heck Crosscoupling Reactions. Acta Chem. Malaysia. 2022;6(1):35–42. [Google Scholar]
  6. Keypour H. et al., Post-synthetic modification of dual-porous UMCM-1-NH2 with palladacycle complex as an effective heterogeneous catalyst in Suzuki and Heck coupling reactions. J. Organomet. Chem. 2023:122646. doi: 10.1016/j.jorganchem.2023.122646. [DOI] [Google Scholar]
  7. Cao J. Li X. Tian H. Metal-organic framework (MOF)-based drug delivery. Curr. Med. Chem. 2020;27(35):5949–5969. doi: 10.2174/0929867326666190618152518. [DOI] [PubMed] [Google Scholar]
  8. Mallakpour S. Nikkhoo E. Hussain C. M. Application of MOF materials as drug delivery systems for cancer therapy and dermal treatment. Coord. Chem. Rev. 2022;451:214262. doi: 10.1016/j.ccr.2021.214262. [DOI] [Google Scholar]
  9. Keypour H. Kouhdareh J. Alavinia S. Maryamabadi A. Application of Co3(BTC)2·12H2O as a Metal-Organic Framework in Controlled Uptake-Release of Oxaliplatin. Acta Chem. Malaysia. 2022;6(2):100–105. [Google Scholar]
  10. Liédana N. et al., The template role of caffeine in its one-step encapsulation in MOF NH 2-MIL-88B (Fe) J. Mater. Chem. B. 2014;2(9):1144–1151. doi: 10.1039/C3TB21707H. [DOI] [PubMed] [Google Scholar]
  11. Wu S. et al., A review of performance optimization of MOF-derived metal oxide as electrode materials for supercapacitors. Int. J. Energy Res. 2019;43(2):697–716. doi: 10.1002/er.4232. [DOI] [Google Scholar]
  12. Tahmasebi E. et al., Application of mechanosynthesized azine-decorated zinc (II) metal–organic frameworks for highly efficient removal and extraction of some heavy-metal ions from aqueous samples: a comparative study. Inorg. Chem. 2015;54(2):425–433. doi: 10.1021/ic5015384. [DOI] [PubMed] [Google Scholar]
  13. Li J.-R. Kuppler R. J. Zhou H.-C. Selective gas adsorption and separation in metal–organic frameworks. Chem. Soc. Rev. 2009;38(5):1477–1504. doi: 10.1039/B802426J. [DOI] [PubMed] [Google Scholar]
  14. Czaja A. U. Trukhan N. Müller U. Industrial applications of metal–organic frameworks. Chem. Soc. Rev. 2009;38(5):1284–1293. doi: 10.1039/B804680H. [DOI] [PubMed] [Google Scholar]
  15. Cui W. G. Hu T. L. Bu X. H. Metal–organic framework materials for the separation and purification of light hydrocarbons. Adv. Mater. 2020;32(3):1806445. doi: 10.1002/adma.201806445. [DOI] [PubMed] [Google Scholar]
  16. Yin Z. et al., Recent advances in post-synthetic modification of metal–organic frameworks: New types and tandem reactions. Coord. Chem. Rev. 2019;378:500–512. doi: 10.1016/j.ccr.2017.11.015. [DOI] [Google Scholar]
  17. Yu Q. et al., Advances in luminescent metal-organic framework sensors based on post-synthetic modification. TrAC, Trends Anal. Chem. 2020;129:115939. doi: 10.1016/j.trac.2020.115939. [DOI] [Google Scholar]
  18. Akhbari K. Morsali A. Modulating methane storage in anionic nano-porous MOF materials via post-synthetic cation exchange process. Dalton Trans. 2013;42(14):4786–4789. doi: 10.1039/C3DT32846E. [DOI] [PubMed] [Google Scholar]
  19. Marpaung F. et al., Metal–organic framework (MOF)-derived nanoporous carbon materials. Chem.–Asian J. 2019;14(9):1331–1343. doi: 10.1002/asia.201900026. [DOI] [PubMed] [Google Scholar]
  20. Kim M. et al., MOF-derived nanoporous carbons with diverse tunable nanoarchitectures. Nat. Protoc. 2022:1–42. doi: 10.1038/s41596-022-00718-2. [DOI] [PubMed] [Google Scholar]
  21. Zhu C. et al., Highly efficient nonprecious metal catalysts towards oxygen reduction reaction based on three-dimensional porous carbon nanostructures. Chem. Soc. Rev. 2016;45(3):517–531. doi: 10.1039/C5CS00670H. [DOI] [PubMed] [Google Scholar]
  22. Gotico P. Halime Z. Aukauloo A. Recent advances in metalloporphyrin-based catalyst design towards carbon dioxide reduction: from bio-inspired second coordination sphere modifications to hierarchical architectures. Dalton Trans. 2020;49(8):2381–2396. doi: 10.1039/C9DT04709C. [DOI] [PubMed] [Google Scholar]
  23. Xia W. et al., Metal–organic frameworks and their derived nanostructures for electrochemical energy storage and conversion. Energy Environ. Sci. 2015;8(7):1837–1866. doi: 10.1039/C5EE00762C. [DOI] [Google Scholar]
  24. Kouhdareh J. et al., Pd (II)-immobilized on a novel covalent imine framework (COF-BASU1) as an efficient catalyst for asymmetric Suzuki coupling. J. Mol. Struct. 2023;1273:134286. doi: 10.1016/j.molstruc.2022.134286. [DOI] [Google Scholar]
  25. Camasso N. M. Sanford M. S. Design, synthesis, and carbon-heteroatom coupling reactions of organometallic nickel (IV) complexes. Science. 2015;347(6227):1218–1220. doi: 10.1126/science.aaa4526. [DOI] [PubMed] [Google Scholar]
  26. Aghayee M. et al., Synthesis and characterization of a novel magnetic nano-palladium Schiff base complex: application in cross-coupling reactions. Appl. Organomet. Chem. 2016;30(8):612–618. doi: 10.1002/aoc.3477. [DOI] [Google Scholar]
  27. Keypour H. et al., Synthesis of magnetically recyclable Fe3O4@[(EtO) 3Si–L1H]/Pd (II) nanocatalyst and application in Suzuki and Heck coupling reactions. Appl. Organomet. Chem. 2017;31(2):e3558. doi: 10.1002/aoc.3558. [DOI] [Google Scholar]
  28. Habibi D. et al., A green and facile approach for the synthesis of N-monosubstituted ureas in water: Pd catalyzed reaction of arylcyanamides (an unexpected behavior of electron withdrawing groups) Polyhedron. 2018;151:520–529. doi: 10.1016/j.poly.2018.05.049. [DOI] [Google Scholar]
  29. Balali M. et al., Palladium Supported on Schiff Base Functionalized Magnetite Nanoparticles as an Efficient Catalyst for Coupling Reactions. Inorg. Chem. Res. 2021;5(1):82–93. [Google Scholar]
  30. Keypour H. Kouhdareh J. Alavinia S. Rezaei M. t. Synthesis of Magnetic Nano Catalyst Using Dopamine Functionalized Magnetic Nano Particles and Investigation of Its Properties in Mizoroki–Heck Cross-Coupling Reactions. Acta Chem. Malaysia. 2023;7(1):16–22. [Google Scholar]
  31. Keypour H. Noroozi M. Hydrogenation of benzene in gasoline fuel over nanoparticles (Ni, Pt, Pd, Ru and Rh) supported fullerene: Comparison study. J. Appl. Chem. 2016;10:31–42. [Google Scholar]
  32. Keypour H. Application of Response Surface Methodology for Catalytic Hydrogenation of Nitrobenzene to Aniline Using Ruthenium Supported Fullerene. Nanocatalyst. 2015;34:21–32. [Google Scholar]
  33. Kouhdareh J. et al., Immobilization of Ag and Pd over a novel amide based covalent organic framework (COF-BASU2) as a heterogeneous reusable catalyst to reduce nitroarenes. Inorg. Chim. Acta. 2023;545:121251. doi: 10.1016/j.ica.2022.121251. [DOI] [Google Scholar]
  34. Karimi B. et al., Highly efficient aerobic oxidation of alcohols using a recoverable catalyst: the role of mesoporous channels of SBA-15 in stabilizing palladium nanoparticles. Angew. Chem., Int. Ed. 2006;45(29):4776–4779. doi: 10.1002/anie.200504359. [DOI] [PubMed] [Google Scholar]
  35. Enders D. Niemeier O. Henseler A. Organocatalysis by N-heterocyclic carbenes. Chem. Rev. 2007;107(12):5606–5655. doi: 10.1021/cr068372z. [DOI] [PubMed] [Google Scholar]
  36. Roughley S. D. Jordan A. M. The medicinal chemist's toolbox: an analysis of reactions used in the pursuit of drug candidates. J. Med. Chem. 2011;54(10):3451–3479. doi: 10.1021/jm200187y. [DOI] [PubMed] [Google Scholar]
  37. Hartwig J. F. Carbon–heteroatom bond-forming reductive eliminations of amines, ethers, and sulfides. Acc. Chem. Res. 1998;31(12):852–860. doi: 10.1021/ar970282g. [DOI] [Google Scholar]
  38. Yu C.-X. et al., Selective MT2 melatonin receptor antagonist blocks melatonin-induced antinociception in rats. Neurosci. Lett. 2000;282(3):161–164. doi: 10.1016/S0304-3940(00)00883-1. [DOI] [PubMed] [Google Scholar]
  39. Rajmohan L. and Mohan V., Repaglinide: the prandial glucose regulator-a new class of oral antidiabetic drugs, Proceedings of Scientific Sessions, APICON 2000, 2000, vol. 10, pp. 519–521 [Google Scholar]
  40. Ma D. Cai Q. Copper/amino acid catalyzed cross-couplings of aryl and vinyl halides with nucleophiles. Acc. Chem. Res. 2008;41(11):1450–1460. doi: 10.1021/ar8000298. [DOI] [PubMed] [Google Scholar]
  41. Monnier F. Taillefer M. Catalytic C–C, C–N, and C–O Ullmann-Type Coupling Reactions. Angew. Chem., Int. Ed. 2009;48(38):6954–6971. doi: 10.1002/anie.200804497. [DOI] [PubMed] [Google Scholar]
  42. Surry D. S. Buchwald S. L. Diamine ligands in copper-catalyzed reactions. Chem. Sci. 2010;1(1):13–31. doi: 10.1039/C0SC00107D. [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Olcay E. et al., Oral toxicity of pefloxacin, norfloxacin, ofloxacin and ciprofloxacin: comparison of biomechanical and histopathological effects on Achilles tendon in rats. J. Toxicol. Sci. 2011;36(3):339–345. doi: 10.2131/jts.36.339. [DOI] [PubMed] [Google Scholar]
  44. Iacovino R. et al., β-Cyclodextrin inclusion complex to improve physicochemical properties of pipemidic acid: Characterization and bioactivity evaluation. Int. J. Mol. Sci. 2013;14(7):13022–13041. doi: 10.3390/ijms140713022. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Kwan E. E. et al., Concerted nucleophilic aromatic substitutions. Nat. Chem. 2018;10(9):917–923. doi: 10.1038/s41557-018-0079-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Liu C. et al., Celecoxib alleviates nonalcoholic fatty liver disease by restoring autophagic flux. Sci. Rep. 2018;8(1):1–10. doi: 10.1038/s41598-018-22339-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Islam S. M. et al., Highly efficient recyclable polymer anchored palladium catalyst for CC and CN coupling reactions. J. Mol. Catal. A: Chem. 2013;366:321–332. doi: 10.1016/j.molcata.2012.10.011. [DOI] [Google Scholar]
  48. Esfandiary N. Bagheri S. Heydari A. Magnetic γ-Fe2O3@ Cu-LDH intercalated with Palladium Cysteine: An efficient dual nano catalyst in tandem CN coupling and cyclization progress of synthesis quinolines. Appl. Clay Sci. 2020;198:105841. doi: 10.1016/j.clay.2020.105841. [DOI] [Google Scholar]
  49. Alavi M. A. et al., Ultrasound and modulation assisted synthesis of {[Cu2(BDC-NH2)2(dabco)]·DMF·3H2O} nanostructures; New precursor to prepare nanorods and nanotubes of copper (II) oxide. Ultrason. Sonochem. 2015;22:349–358. doi: 10.1016/j.ultsonch.2014.04.017. [DOI] [PubMed] [Google Scholar]
  50. Gupta N. K. et al., Fabrication of Cu(BDC)0.5(BDC-NH2)0.5 metal-organic framework for superior H2S removal at room temperature. Chem. Eng. J. 2021;411:128536. doi: 10.1016/j.cej.2021.128536. [DOI] [Google Scholar]
  51. Kurisingal J. F. et al., Facile green synthesis of new copper-based metal–organic frameworks: Experimental and theoretical study of the CO2 fixation reaction. ACS Sustainable Chem. Eng. 2020;8(29):10822–10832. [Google Scholar]
  52. Kumar R. et al., Regioselective Mannich bases of pyrrole-2-carbaldehyde and binuclear copper (II) complexes of bis (iminopyrrolyl) ligand containing the piperazine ring. Inorg. Chim. Acta. 2016;445:70–78. doi: 10.1016/j.ica.2016.02.023. [DOI] [Google Scholar]
  53. Skoog D. A., Holler F. J. and Crouch S. R., Instrumental analysis, Brooks/Cole, Cengage Learning, Belmont, 2007, vol. 47 [Google Scholar]
  54. Gorski C. A. Scherer M. M. Determination of nanoparticulate magnetite stoichiometry by Mossbauer spectroscopy, acidic dissolution, and powder X-ray diffraction: A critical review. Am. Mineral. 2010;95(7):1017–1026. doi: 10.2138/am.2010.3435. [DOI] [Google Scholar]
  55. Coats A. Redfern J. Thermogravimetric analysis. A review. Analyst. 1963;88(1053):906–924. doi: 10.1039/AN9638800906. [DOI] [Google Scholar]
  56. Stokes D., Principles and practice of variable pressure/environmental scanning electron microscopy (VP-ESEM), John Wiley & Sons, 2008 [Google Scholar]
  57. Corbari L. et al., Iron oxide deposits associated with the ectosymbiotic bacteria in the hydrothermal vent shrimp Rimicaris exoculata. Biogeosciences. 2008;5(5):1295–1310. doi: 10.5194/bg-5-1295-2008. [DOI] [Google Scholar]
  58. Ratkanthwar K., et al., Schlenk techniques for anionic polymerization, Anionic Polymerization: Principles, Practice, Strength, Consequences and Applications, 2015, pp. 3–18 [Google Scholar]
  59. Sajjadi M. Nasrollahzadeh M. Ghafuri H. Cu (II)-N-benzyl-amino-1H-tetrazole complex immobilized on magnetic chitosan as a highly effective nanocatalyst for CN coupling reactions. J. Organomet. Chem. 2021;950:121959. doi: 10.1016/j.jorganchem.2021.121959. [DOI] [Google Scholar]
  60. Khorsandi Z. et al., Sustainable synthesis of potential antitumor new derivatives of Abemaciclib and Fedratinib via CN cross coupling reactions using Pd/Cu-free Co-catalyst. Mol. Catal. 2022;517:112011. doi: 10.1016/j.mcat.2021.112011. [DOI] [Google Scholar]
  61. Panahi F. et al., Immobilized Pd nanoparticles on silica-starch substrate (PNP-SSS): Efficient heterogeneous catalyst in Buchwald–Hartwig C–N cross coupling reaction. J. Organomet. Chem. 2017;851:210–217. doi: 10.1016/j.jorganchem.2017.09.037. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

RA-013-D3RA01020A-s001
RA-013-D3RA01020A-s001.pdf (2MB, pdf)

Articles from RSC Advances are provided here courtesy of Royal Society of Chemistry

RESOURCES